Dampers dampen (dissipate) the kinetic energy that has been loaded on them. If explanation needs to be made in terms of force and displacement instead of energy, it can be said that, the force applied to the structure by the damper between two mounting points of the damper opposes the relative displacement between two mounting points of the device and hence leads to reduced displacement and thus reduced damage in the structure to which it is mounted. This force is referred to as the reaction force of the damper. Damping in hysteretic dampers is obtained by using a metal that will yield, develop plastic strain and act as a hysteretic energy-dissipating element.
Deployment of energy dissipation devices in building frames is a well-known practice. These devices include viscous dampers, hysteretic dampers, friction-based energy dissipaters and buckling-restraint braces (BRB). Among the steel dampers developed for use in braced frames, the most well-known is the added damping and stiffness (ADAS) elements and its variation, triangular-plate added damping and stiffness (TADAS). ADAS is composed of a series of X-shaped plates clamped and fixed at top and bottom through a bolted connection. Full-scale tests have shown advantages of incorporation of ADAS dampers in terms of reduction of damage in primary structural members, reduction of inter-story deformations at minor and moderate level earthquakes and stable hysteretic behavior of the bracing system. E-shaped and C-shaped elements are another type of plate-bending metallic dampers for Chevron-type bracing systems. Round-hole and double X-shaped dampers also belong to this class of dissipating elements. These two dampers also are of plate-bending type. Another type of plate-bending based damper is the Steel Slit Damper, fabricated from a standard structural wide-flange section with a number of slits cut from the web. Bucking-restraint brace (BRB) is another type of energy dissipation element used in braced frames. In a BRB the brace is encased in a mortar-filled steel tube, while being detached from the mortar using some ‘un-bonding’ agent. The overall assembly is an element in which the inner steel core is free to slide and thus free to deform axially independent of the outer section, while in bending their flexural resistance is added, producing a section stiff in flexure and thus strong against buckling. The subject of the present invention, torsional hysteretic damper, is a mechanical device designed to utilize torsional yielding of cylindrical energy dissipaters (EDs) made of ductile steel to dissipate the imposed energy through seismic movements in a structure. Torsional hysteretic damper converts the translational motion imposed on it at its two connection points into twisting at the energy dissipaters which are designed to yield in torsion and dissipate energy.